I do agree with all of what has already been explained in this thread, but I still saw something odd that I haven't seen discussed----
There is a weapon in Mideel. It is a rod called something like "crystal rod". You can buy it. Umm.....?

I do believe that something drastically changed in the middle of making the game concerning Aeris and her death. I think that she was always supposed to die, but the event was to come later in the story. The innerworkings of the game have tons of evidence.